That which curves and that which is straight

A Piece of Mars: The long meandering lines snaking across the image (3.2×1.8 km or 2×1.1 mi across) are inverted channels. They are river deposits that once were the lowest part of the landscape (rivers always are), but then the water dried up and wind erosion took over. The river channels were more resistant to erosion and so now they stand above the rest of the terrain. The wind left behind straight, streamlined hills called yardangs. Given enough time, the wind will scrape at the surface until both the yardangs and the river channels are gone, but for now there’s a beautiful landscape. (HiRISE PSP_002424_1765 NASA/JPL/Univ. of Arizona)